1. Field of the Invention
The present invention generally relates to image pickup devices capable of picking up images while electronically enlarging the same. More particularly, the present invention relates to an image pickup device capable of picking up images while electronically enlarging the same which includes a CCD image sensor as an image pickup element and is used, for example, in a video camera or a video tape recorder with a built-in camera.
2. Description of the Prior Art
FIG. 23 is a schematic block diagram showing a conventional image pickup device capable of picking up images while electronically enlarging the same by two times. Referring to the diagram, a timing pulse generating circuit 109 generates a timing pulse for driving a CCD image sensor 101, a signal for controlling an analog switch 104, and several other pulses required for a signal processing circuit 106, in synchronization with synchronizing signals generated from a synchronizing signal generator 110. A switch SW1 for switching between the normal image pickup and the enlarged image pickup is connected to the timing pulse generating circuit 109. The timing pulse generating circuit 109 changes periods of a horizontal transfer pulse and a vertical transfer pulse according to operation of the switch SW1.
The horizontal transfer pulse generated from the timing pulse generating circuit 109 is applied to the CCD image sensor 101 through a horizontal driver 111 and the vertical transfer pulse is applied to the CCD image sensor 101 through a vertical driver 112. Video signals outputted from the CCD image sensor 101 are applied to a sample and hold (S/H) circuit 102 to be sampled and held, and then applied to a 1H delay circuit 103 and the analog switch 104. The 1H delay circuit 103 delays the video signals 1H (one horizontal scanning period) for application to the analog switch 104. The analog switch 104 is responsive to a switching signal from the timing pulse generating circuit 109 for selecting output of either the sample and hold circuit 102 or the 1H delay circuit 103 and applying the selected one to the signal processing circuit 106. The signal processing circuit 106 includes sample and hold circuits, processing circuits and an encoder for converting the video signals from the analog switch 104 into primary color signals R, G and B.
In the conventional image pickup device constituted as described above, when the enlarging image pickup by two times is done with the switch SW1 closed, the timing pulse generating circuit 109 applies the horizontal and vertical transfer pulses that have frequencies half those of the normal image pickup, to the CCD image sensor 101 through the horizontal driver 111 and the vertical driver 112, respectively. Since frequencies of the horizontal and vertical transfer pulses become 1/2 with respect to those of the normal image pickup, it takes twice the time, or 2H to output charges of one horizontal line in the CCD image sensor 101. Charges corresponding to 1H of the 2H are unnecessary, so that they are replaced by required signals of 1H before they have been delayed by the 1H delay circuit 103. This replacement is effected by the analog switch 104. The unnecessary charges in the vertical direction (corresponding to a 1/2 area of a standard screen) are deleted by fast vertical transfer performed during a vertical blanking period so that they are not outputted as the video signals from the CCD image sensor 101.
In the image pickup device shown in FIG. 23, the 1H delay circuit 103 may be implemented, for example, as a CCD 1H delay circuit. Since the video signals entered in the signal processing circuit 106 have not yet undergone any processing, however, the signal processing circuit 106 will exhibit a very large dynamic range. On the other hand, such a delay circuit 103 as 1H constituted by a CCD or the like does not have a large dynamic range. Therefore, the use of such an element is impossible and thus miniaturization of the circuit cannot be achieved. Additionally, in the conventional image pickup device shown in FIG. 23, a complementary color filter employed in the CCD image sensor 101 is limited to a vertical stripe filter only, so that a diced filter is unacceptable.
FIG. 24 is a schematic block diagram showing part of a conventional image pickup device for the normal image pickup in which a diced filter is used as the complementary color filter, and FIG. 25 is a diagram showing relationship between line sequential color-difference signals C.sub.OH and 1H-delayed C.sub.1H, an R channel component (R-Y) and a B channel component (B-Y).
In the image pickup device shown in FIG. 24, video signals outputted from a sample and hold circuit 102 are applied to an OB clamp circuit 108 where their optical black level is clamped, and then applied to sample and hold circuits 113 and 114. The sample and hold circuits 113 and 114 separate color components from the video signals to apply them to a signal processing circuit 115. A processed line sequential color-difference signal C.sub.OH is applied to a 1H delay circuit 116 and an analog switch 117. The 1H delay circuit 116 delays the line sequential color-difference signal C.sub.OH by 1H to obtain a C.sub.1H which is applied to the analog switch 117. The analog switch 117 outputs an R channel component (R-Y) and a B channel component (B-Y) out of the line sequential color-difference signals C.sub.OH and C.sub.1H.
In the image pickup device constituted as described above, the CCD image sensor 101 which has a diced filter employed therein outputs a color-difference signal for every 1H line-sequentially. To interpolate the line sequential color-difference signals, the 1H delay circuit 116 and the analog switch 117 are used. The relationship between the line sequential color-difference signals C.sub.OH and C.sub.1H, the R channel component (R-Y) and the B channel component (B-Y), in this case, will be as shown in FIG. 25.
FIG. 26 is a block diagram of the image pickup device shown in FIG. 24 with an additional enlarging image pickup function. FIG. 27 is a diagram showing relationship between the line sequential color-difference signals C.sub.OH, C.sub.1H and C.sub.2H, the R channel component (R-Y) and the B channel component (B-Y) in the image pickup device shown in FIG. 26.
Referring to FIG. 26, between an OB clamp circuit 108 and sample and hold circuits 113 and 114, there are connected a 1H delay circuit 103 and an analog switch 104. Further, between a 1H delay circuit 116 and an analog switch 117, there are connected a 1H delay circuit 118 and an analog switch 119. The 1H delay circuit 103 and the analog switch 104 are provided for replacing unnecessary charges of 1H by required signals of 1H before in the enlarged image pickup through the same operation as in FIG. 23. The 1H delay circuit 118 and the analog switch 119 are provided to interpolate the color-difference signals in the enlarged image pickup. The relationship between the line-sequential color-difference signals C.sub.OH, C.sub.1H and C.sub.2H and the R and B channel components (R-Y) and (B-Y) in such an image pickup device will be as shown in FIG. 27. Meanwhile, in the normal image pickup, the analog switch 119 selects output of the 1H delay circuit 116. Further in the enlarging image pickup, it selects output of the 1H delay circuit 118.
As described above, the image pickup device shown in FIG. 26 allows for the enlarging image pickup as well as the normal image pickup even when a complementary color diced filter is used therein. As will be apparent from FIG. 26, however, provision of three 1H delay circuits is required. When they are implemented as CCD 1H delay circuits, however, costs are too expensive. Further, for a luminance signal, the same signal appears over two lines in the vertical direction, and for the color-difference signal, the same signal appears over four lines. This produces indentation of a diagonal line or a curb and thus a mosaic picture, considerably deteriorating the picture quality.
Furthermore, in the image pickup device with the conventional enlarging image pickup function, the same vertical are horizontal aperture circuits are used in the normal and enlarging image pickups. Since in the enlarging image pickup, however, the same signal appears over two lines in the vertical direction, good contour correction cannot be made if the same vertical aperture circuit is used as is used normal image pickup. Further, since in the enlarging image pickup, the horizontal transfer pulse of the CCD image sensor 101 has a 1/2 frequency relative to that in the normal image pickup, signal a band becomes 1/2. Therefore, again good contour correction cannot be made if the same horizontal aperture circuit as in the normal image pickup is used. Additionally, if the same mix amount of aperture is used in the enlarging and the normal image pickups, there arises a problem that proper mix amount cannot be provided for each case.